1. Field of the Invention
The invention relates generally to processes for balancing piano key mechanisms and similar mechanisms for stringed keyboard instruments and particularly to the balancing of individual key mechanisms forming a keyboard to create a consistent "feel" of the keys.
2. Description of the Prior Art
In the manufacture of stringed keyboard instruments such as pianos and the like, a critical manufacturing procedure resulting in the "feel" of the action of the instrument is known as "key balancing". Key balancing occurs in the manufacturing process after the action is assembled and working. The key balancing procedure is of utmost importance due to the fact that stringed keyboard instruments using key activated mechanical systems, generally referred to as "actions", for production of musical tone of varied intensity from the strings and soundboard of the instrument, require a consistent pressure for depression of the keys across the keyboard. For example, a pianist must "feel" a consistent pressure necessary to depress each piano key so that the pianist can easily play a series of notes at the same tone volume by application of the same pressure to each key. Therefore, when touch is uniform, that is, when every key "feels" alike, the piano is easier to play and the musical result is more satisfying. In the event that each key requires that a different pressure be applied by the pianist to play that key at a given volume, the pianist must learn that pressure necessary to apply to each key, a difficult task at best even for the most accomplished of musicians. Further, the overall level of touch resistance which is to be applied to the keys must not be too light or too heavy or the pianist will otherwise encounter difficulty in controlling the sound of the piano.
Key balancing processes of the prior art involve the placement of lead counterweights called "keyleads" into the front of a key lever of each piano key mechanism. This weighting of each key lever attenuates the upwards force at the playing end of the key mechanism exerted by the weight and the leverage of the action parts resting on the back of the key lever. These parts of the action include a hammer for each key mechanism which is attached to a shank pivoted at a hammer shank flange. The weight of the shank and the hammer attached thereto exerts a downward force on a part known as the wippen at a contact point known as the knuckle contact point. An action part known as a knuckle is attached to the hammer shank and that point at which the knuckle contacts the wippen is known as the knuckle contact point. The downward force exerted by the hammer and the shank of the hammer combines with the weight of the wippen, pivoted at a flange of the wippen, to exert a downward force on the back of the key at a point known as the capstan contact point, this downward force translating through the key lever to an upwardly directed force at the playing end of the key lever. The weight of the hammer at the end of the hammer shank exerts considerable influence on the amount of keylead used in the key. Maximum keylead usage occurs on the bass side of the keyboard where the hammers of the respective keys are heaviest. Keylead usage dwindles down to little or none in the treble side of the keyboard where hammers are lightest. Without keyleads, the amount of force required to depress the keys would be too great to produce an appropriate feel to the keys on playing.
A conventional method for key balancing which has been used by piano manufacturers for many years involves the placement of a specified amount of weight, known as the "downweight" and usually being set at approximately 50 grams, on the playing end of the key lever at a specified point, i.e., the measuring point. An appropriate number of keyleads are placed on top of the key lever between the measuring point and the key lever balance point. In some cases, keylead may also be used on the back of the key lever balance point. The keyleads are then slid in small increments along the key lever until positions are found which will cause the key to go slowly down at the front and the hammer to slowly rise at the back of the mechanism, thereby indicating that the specified downweight has been provided. A weight value known as the "upweight", that is, the amount of weight which the depressed key can slowly lift, may be then checked to determine whether a sufficient lifting force exists in order to return the key to rest after being played. Keylead positions are then marked, holes drilled in the key at the marks, and the keyleads permanently mounted in the holes. While the manufacturing procedure just described has been common in the art for a number of years, this prior art method of key balancing is significantly flawed. These flaws result in part from the fact that these newly manufactured actions which are being key balanced have new parts and felts. In particular, the key bushings tend to be tight when the action is new. In fact, piano manufacturers consider this tendency to be normal since it is actually desired by the manufacturer for the key bushings to be as tight as possible while still working freely in order to prevent premature wear in the field. If a particular key bushing is too tight at the time of key balancing in the factory, then more keylead will be placed in that key in order to overcome the resulting high friction and to start the key moving downwardly in achieving a specified downweight. When the key bushing becomes free, that is, more loose, at a later time and therefore produces less friction, the greater amount of lead weight in the key remains, thereby causing the key to have a significantly higher inertia compared to adjoining keys. Accordingly, the prior art practice of balancing keylead against high friction which usually exists during key balancing occurring in the manufacturing process creates chaotic inconsistencies in downweight measurements once the piano is out of the factory and in use. It is thus readily seen that the downweight measurement, the primary key balancing indicator in prior art manufacturing procedures, has a friction component which creates wide and inconsistent results.
The commonly accepted and widely used prior art key balancing technology presents an additional problem which relates to the inconsistent use of key balancing weights. For example, when a key is struck during the act of playing a piano, the inertia of the key becomes the significant force resistance which is felt by the pianist. The force, exerted by the finger of the pianist, needed to overcome key inertia can be in the hundreds or even thousands of grams. The amount of force required to overcome key inertia is proportional to the sum of inertial moments within each key. The inertial moment of a part referred to as the keystick, within which are mounted the key balancing weights, is a significant component of inertia. When the use of key balancing weights varies widely as occurs in the prior art, the moment of inertia of the keystick is likely to be inconsistent from note to note with the result being an uneven playing quality. Another problem which results from the presently used method for key balancing results from the fact that the method itself mirrors inconsistencies in the weight and/or leverage of the parts. Small inconsistencies in the weight of the parts and in the length of the lever arms of the parts in the various parts of each key mechanism add up to create significant random inconsistency from note to note in the amount of upward force exerted at the front of each key. Even when the keys are balanced under ideal conditions, that is, with uniform friction from key to key, these inconsistencies result in varied amounts of keylead being used from note to note. One result of this fact is a significant variation in the inertial moments within each key which create an uneven playing quality, thereby causing the pianist to compensate for the inconsistencies and thus causing the piano to be more difficult to control and therefore to play.
Still another problem inherent in the prior art key balancing process results from the fact that the hammers and parts wear out as the instrument is played over time, it then being necessary for the hammers and associated parts to be replaced. Since replacement parts invariably provide a new and entirely different set of weight and leverage inconsistencies than were originally present in the manufacture of the instrument, the keys must be rebalanced each time new parts are installed in order to maintain even those standards inherent in the prior art key balancing process.
Another prior art key balancing process is utilized with certain types of pianos which use a wippen support spring combined with keyleads to balance the action. This wippen support spring reduces the downward force exerted by the combined weight of the parts of the action on the capstan of the key mechanism. Wippen support spring actions typically require less keylead usage and result in keysticks having substantially lower inertial moment and which thereby require substantially lower force to propel the key to a given acceleration. When the key is played with rapid repetition, the repetition spring need not accelerate as much mass in the keystick and a faster, more solid repetition is possible. However, the prior art does not provide for a method specifying the proportion of wippen support spring tension to the amount of keylead usage, thereby resulting in underutilization of a useful application of wippen support springs.
The metrology of the prior art is therefore seen to be limited to the measured values of downweight and upweight along with their respective calculated weight and friction components. Downweight is the minimum amount of weight that, when placed on the measuring point of the key, causes the key to go down slowly. Upweight is the amount of weight that, when placed on the measuring point of the depressed key, allows the key to slowly lift. The weight component of downweight and upweight is known as the balance weight and is equal to the amount of weight placed on the measuring point of the key which counterbalances the upward force exerted by the weight and leverage of the parts of the action. The friction component is known as the friction weight and is the amount of weight which when added to the balance weight causes the key to move slowly downwardly or when subtracted from the balance weight allows the key to slowly lift. The balance weight and friction weight are determined by calculation with the balance weight being the average of downweight and upweight. Friction weight is calculated as downweight minus upweight with the resulting value being divided by two. However, even the most ideal realization of the prior art methodology of key balancing during manufacture to produce a uniformly consistent balance weight is too time consuming for practical application in the manufacture of pianos and similar stringed keyboard instruments.
Prior patents have addressed the problems referred to above. For example, Hardesty et al, in U.S. Pat. No. 4,286,493 attempts to provide a graduated leverage piano action by reducing overall touch forces and by causing the touch forces at one end of the keyboard to be substantially equal to the touch forces at the other end of the keyboard. However, Hardesty et al provide a piano action which reduces playing forces and which does not provide for a balancing of piano keys and the like to eliminate the problems referred to hereinabove which continue to plague the industry in the manufacture of keyboard actions and in the refurbishment of actions which must be at least in part replaced due to wear.
Accordingly, a long-felt need continues to exist in the art for methodology useful in the manufacture and/or refurbishment of keyboard actions to produce a consistent "feel" of the action when played and which can be incorporated into the manufacture of stringed keyboard instruments in a practical, timewise manner.